Retractable headlights in a vehicle are opened and closed by motor and gear mechanism contained within a housing. While the mechanism runs for very little total time over the life of the vehicle, its housing has a constant exposure to the ambient, from which it must be sealed in order to protect the motor. As a practical matter, the housing needs an opening with a removable cover to allow easy access for installation of the motor. As a consequence, there is a seam between the edge of the housing opening and the cover, which represents a potential leak path from the ambient to the internal volume of the housing, and which must be sealed. The conventional seal is a simple gasket clamped between the cover and housing to fill and block the seam. Complicating the sealing task, however, is the fact that the internal volume of the housing is subject to fairly large temperature differentials relative to ambient, due to the heating of the motor, and temperature changes in the ambient itself. The consequent relative expansion and contraction of the air within the housing can lead to a pressure differential relative to ambient. While positive pressure differentials caused by heating of the air in the enclosed volume are not generally a problem, the negative pressure differential that occurs afterward due to cooling can tend to draw ambient air, and thus water vapor, through the seam. Conventional gasket seals do nothing to compensate for this potential pressure differential.